Maximizing data return for the Europa lander: A trade study in the application of CCSDS protocols

Abstract

In support of NASA, Caltech's Jet Propulsion Laboratory and The Johns Hopkins Applied Physics Laboratory are studying concepts for two missions to explore Europa: a multiple flyby spacecraft and a surface lander. This paper analyzes the use of packetized, multi-hop, multi-path communications protocols for the Europa lander concept and assesses their potential for reducing power requirements while increasing data return. Analysis includes three protocols standardized by the Consultative Committee for Space Data Systems (CCSDS): the CCSDS File Delivery Protocol (CFDP), the Bundle Protocol (BP), and the Licklider Transmission Protocol (LTP). A spacecraft may implement a networking stack of one or more of these protocols, with each of these stacks exhibiting different strengths and weaknesses. We present heuristic and analytical methods for evaluating protocol performance including a priori computations of protocol overheads, Monte-Carlo analysis across bit error rates and packet sizes, and high fidelity simulations. Quantitative metrics such as retransmission efficiency, packet overhead, and end-to-end transaction duration characterize individual protocol options. Qualitative metrics such as cost of ownership, mission operations complexity, and computational processing load characterize the mission impacts of various networking stacks. We generate results using anticipated mission link characteristics, data volumes, and network geometries and provide recommendations relating to the value of software protocols and multi-protocol networking stacks. Results demonstrate that each candidate protocol combination can be tuned to within 15% of optimal performance over links of up to 10−4 bit error rate, although achieving this efficiency with solely CFDP incurs up to 800% greater computational processing load versus the other stacks. We conclude multiprotocol stacks separate concerns when optimizing performance for multiple stakeholders. A CFDP/BP/LTP networking stack solves a joint optimization problem where CFDP can be tuned for onboard data operations, BP can be used to provide standardized priority and store-and-forward operations, and LTP can be tuned for retransmission and acknowledgement. This approach enables efficient end-to-end communications for the Europa lander concept that maximizes data return with minimal power requirements.